This invention relates to the general field of screening systems and particularly to screening systems with a screen or sieve having openings and devices used to free the screen from material blocking or plugging the openings.
In mining and related fields, screening systems are used to separate fine pieces of material from larger pieces of material. These screening systems generally include some number of screen panels which sit on a framework of steel girders. When the steel girders are jostled and moved around, fine material on the screen panels drops through the openings in the screen and larger pieces of material bounce off the screens and off the sides of the screening system, where those larger pieces are collected for further processing.
In some screening applications fine material will begin sticking to the screen surface and build up to the point where fine material bridges over the openings in the screen. This bridging of fine material reduces the size of the openings in the screen (commonly referred to as blinding), which can get progressively worse over time. Once a sufficient percentage of the screen openings is blinded by bridged fine material, the screening system is too ineffective and must be shut down so that the screens can be removed or manually cleaned. This can frequently shut down an entire mining operation or plant, especially if the material being screened is damp or irregularly-shaped.
In addition to the problems with fine material bridging the openings, larger angular or irregular-shaped particles in the material can become lodged in the openings of the screen, blocking it much like blinding. This problem is widely referred to as plugging or pegging. The effects of plugging are very similar to those of blinding.
The mechanical action of a screening system causes some level of G-forces to be exerted on the screen panels. This mechanical action drives the screening process and helps avoid blinding or plugging of the screens, but the speed and stroke of the mechanical action must be within industry standards. If the screening system is running at maximum G-force (maximum referring to the state where an increase in speed will damage the screening system) and plugging or blinding still occurs, there needs to be some other mechanical means to vibrate or impact the screen and keep the screen surface clean.
Some of the screening system manufacturers have tried to solve this plugging and blinding problem with a design that incorporates steel wire baskets attached to the steel girders below every screen panel. These steel wire baskets contain rubber or urethane balls placed within the basket so that when the mechanical action of the screening system is activated, the balls bounce repeatedly off the steel wire baskets and into the bottom of the screen panels to help prevent blinding and plugging. These steel wire baskets wear out easily with abrasive materials being screened, and the frequent replacement of these baskets is time-consuming and expensive. These steel baskets also cannot be retrofitted to older screening systems, but can only be attached to newer screening systems designed to incorporate the baskets.
One design which attempted to solve the problems of the steel basket systems by attaching a beating device such as a plastic ball attached to rubberized arms connected to the frame of a screen panel is disclosed in U.S. Pat. No. 7,416,085. That system addressed many of the problems with the steel basket design, but attaching the beating device directly to the screen panel leads to different problems. New screen panels needed to be created to allow integration with the beating devices, and if one of the two elements is defective or broken, the entire screen panel and beating device unit must be replaced.
Consequently, it would be desirable to come up with a screening system which overcomes these and other problems with prior art systems and can knock loose build-ups of blinding and plugging material while being resilient to the abrasive materials typically screened with these machines.